The larger blood vessels of the body share a common anatomy. The inner lining is the endothelium, followed by subendothelial connective tissue, i.e., laminin, among other constituents, followed by a vascular smooth muscle layer. Finally, there is a connective tissue layer called the adventitia, which contains nerves that supply the muscular layer, as well as nutrient capillaries in the larger blood vessel. In contrast, smaller capillaries consist of little more than a layer of endothelium and occasional connective tissue.
The “endothelium” is a layer of thin, flat cells that lines the interior surface of blood vessels, forming an interface between circulating blood in a lumen of the blood vessel and the rest of a blood vessel wall. Endothelial cells line the entire circulatory system, include the coronary vasculature and capillaries. These cells are involved in a number of regulatory vascular processes, including, vasoconstriction and vasodilation, thrombosis and fibrinolysis, atherosclerosis, angiogenesis, and inflammation and edema. “Vasoconstriction” and “vasodilation” refer to the narrowing and widening of a blood vessel, respectively. “Thrombosis” is the formation of a clot within a blood vessel obstructing the flow of blood throughout the circulatory system. “Fibrinolysis” is the process wherein a fibrin clot formed within a blood vessel is broken down. “Angiogenesis” is the promotion or causation of new blood vessel formation. “Atherosclerosis” is a type of arteriosclerosis (thickening and hardening of arteries) in which cells including smooth muscle cells and macrophages, fatty substances, cholesterol, cellular waste product, calcium and fibrin build up on a blood vessel's inner lining.
The absence of a healthy endothelium or the presence of a diseased endothelium can lead to thrombosis or atherosclerotic plaque build-up. In some medical procedures, the endothelium can become denuded or damaged. For example, the endothelium can become denuded or damaged by an angioplasty procedure or the placement of an implantable medical device such as a stent. “Denuded” refers to the stripping of the endothelium in a blood vessel. In addition, ischemia reperfusion; a myocardial infarction; drugs which are delivered locally, regionally or systemically and which are capable of stripping the endothelium layer; and viruses or bacteria which are capable of stripping the endothelium layer can damage the endothelium. Likewise, regions of diseased vessels, such as atherosclerotic vessels, often have a dysfunctional endothelium.
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease, particularly stenosis. “Stenosis” refers to a narrowing or constriction of the diameter of a vessel. In a typical PTCA procedure, a catheter assembly having a balloon portion is introduced percutaneously into the cardiovascular system of a patient via the brachial or femoral artery to treat stenosis at a lesion site. The catheter assembly is advanced through the coronary vasculature until the balloon portion crosses the occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress the atherosclerotic plaque of the lesion against the artery's inner wall, which dilates the lumen. The balloon is then deflated to allow the catheter to be withdrawn from the patient's vasculature.
The treatment of a diseased site or lesion within a blood vessel can involve both delivery and deployment of a stent. “Delivery” refers to introducing and transporting the stent through a blood vessel to a lesioned site that requires treatment. “Deployment” means expanding the stent within the lumen of a blood vessel at the treatment site. Delivery and deployment of a stent are accomplished by positioning the stent about one end of the catheter, percutaneously inserting the end of the catheter into the blood vessel, advancing the catheter within the lumen of the blood vessel to the treatment site, expanding the stent at the treatment site and removing the catheter from the lumen of the blood vessel. The stent can be balloon-inflatable or self-expanding.